The present invention is directed to new compositions of matter and methods of preparation of high temperature superconducting copper oxides. More particularly, the invention is directed to high temperature superconducting materials with the general formulae of (1) GaSr.sub.2 Ln.sub.1-x M.sub.x Cu.sub.2 O.sub.7.+-.w (M=Ca and Sr, Ln=La, Ce, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Y; 0.2.ltoreq.x.ltoreq.0.4 and w is a small fraction of one) and of (2) Ga.sub.1-y Sr.sub.2 YCu.sub.2+y O.sub.7.+-.w (where y is about 0.65 and less).
All known high temperature superconducting copper oxides have an anisotropic structure containing two-dimensional CuO.sub.2 layers with square planar, square pyramidal and octahedral coordination of the copper to oxygen. These CuO.sub.2 layers are bounded in the third dimension by metal-oxygen layers ("AO" hereinafter) containing large and strongly ionic metal ions (A-Ba, Sr and La-Gd), which form AO-CuO.sub.2 -AO structural blocks. For most superconducting compounds there is frequently more than one CuO.sub.2 layer, separated by metal layers, A' (A'=Ca, lanthanides and Y), which are within the block, and an additional layer of mixed oxidation state cations, covalently bonded to oxygen, between these blocks (e.g., structures based on Cu, Tl, Pb and Bi). In previous attempts, the synthesis of layered copper oxides with more ionic, fixed oxidation state, cations in this additional layer has led to nonsuperconducting materials.
The importance of copper-oxygen layers in the high-temperature (T.sub.c &gt;35K) superconductors was realized in 1986 after the report by Bednorz and Muller on their work in the La-Ba-Cu-O system. The conducting planes (CuO.sub.4/2) of these materials result from the hybridization of the Cu(3d) and O(2p) orbitals which form closely and symmetrically coordinated copper and oxygen atoms in square nets. Other families of superconductors are La.sub.2-x M.sub.x CuO.sub.4 (M=Ca.sup.2+, Sr.sup.2+, Ba2+), Nd.sub.2-x Ce.sub.x CuO.sub.4, YBa.sub.2 Cu.sub.3 O.sub.7-x (Tl, Bi).sub.m (Ba,Sr).sub.2 Ca.sub.n-1 Cu.sub.n O.sub.m+2n+2 (m,n=integers) , Pb.sub.2 Sr.sub.2 LnCu.sub.3 O.sub.8+x (Ln=lanthanides), and La.sub.2-x Sr.sub.x CaCu.sub.2 O.sub.6. All of these compounds can be described as an intergrowth of AO rocksalt layers with ABO.sub.3-x perovskite units and have the general formula (AO).sub.m (ABO.sub.3-x).sub.n where m and n are integers and B is copper. Although no theory on the mechanism of high temperature superconductivity has gained acceptance, the observation of high-temperature superconductivity in this class of layered materials has led to a phenomenological understanding that superconductivity depends on the two-dimensional conducting planes with weak interplane coupling.
The influence of substitutions on superconductivity has been studied in great detail in YBa.sub.2 Cu.sub.3 O.sub.7-x. All lanthanides have been substituted into the eight-coordinate yttrium position. With the exception of praseodymium, superconductivity is preserved. In contrast, the addition of small amounts of a transition or post-transition metal onto either the square-planar or square-pyramidal copper site generally resulted in the loss of superconductivity. Incorporation of the trivalent cations aluminium, iron, and cobalt is believed to occur on the square-planar copper site, whereas chromium or zinc is thought to go into the planes. When large amounts of gallium or aluminium are incorporated, the new single-layer copper compounds LaSrCuAlo.sub.5 and LaSrCuGaO.sub.5 with the brownmillerite (Ca.sub.2 FeA10.sub.5) structure are formed. These structures reflect the preference for tetrahedral coordination by the group thirteen elements. While enormous efforts have been expended in the industry, there have been only several new systems discovered for these types of structures.
It is therefore an object of the invention to provide a novel composition and method of manufacture of high temperature superconducting ceramic.
It is another object of the invention to provide an improved composition of high temperature ceramic superconductor based on GaSr.sub.2 Ln.sub.1-x M.sub.x Cu.sub.2 O.sub.7.+-.w wherein M=Ca and Sr and Ln=La, Ce, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Y.
It is yet a further object of the invention to provide a novel composition of high temperature ceramic superconductor comprised of Ga.sub.1-y Sr.sub.2 YCu.sub.2+y O.sub.7.+-.w wherein y is less than or equal to about 0.65.
It is a further object of the invention to provide a novel method of making a high temperature ceramic superconductor under highly oxidizing atmospheres.
It is an additional object of the invention to provide an improved composition and method of making a gallium containing high temperature ceramic superconductor.
It is yet another object of the invention to provide a novel method of oxidizing a ceramic superconductor to activate the superconducting state of matter.
It is a further object of the invention to provide an improved method of modifying the crystallographic structure of a copper oxide based superconductor to introduce adequate electronic charge into the Cu.sub.2 O layers to establish superconductivity.
It is still another object of the invention to provide a novel method of hole doping of Cu.sub.2 O layers of a high temperature ceramic superconductor.
Other objects and advantages of the invention together with the method of manufacture and product composition will become apparent from the following Detailed Description and Brief Description of the Drawings hereinbelow.